1. Field of the Invention
The invention is related to the field of disk drive systems, and in particular to disk drive systems and circuitry that detect and correlate servo mark sub-patterns to detect servo marks.
2. Statement of the Problem
A disk drive system stores user data in tracks on its disks. The user data in the tracks is interspersed with servo marks and servo data. The disk drive system uses the servo marks to locate both the servo data and selected portions of the user data. Because servo marks are used to locate the other data, servo mark detection is critical to proper system operation.
A servo mark is a bit sequence that is encoded at regular intervals in the tracks on the disks. To detect a servo mark, a head is positioned over a few of the tracks and senses the data encoded on the disk to generate a read signal. The disk drive system converts the read signal into a sequence of samples. The samples are passed through Viterbi circuitry to detect the servo marks.
The Viterbi circuitry assigns probabilities to possible bit sequences and selects the most likely sequence for a match with the servo mark. The Viterbi circuitry typically operates well when the servo marks are aligned from one track to the next. Unfortunately, the Viterbi circuitry may fail during a transition between tracks if the servo marks in the respective tracks are not aligned. The mis-alignment causes a phase shift that the Viterbi circuitry cannot effectively handle. The failure to detect servo marks interrupts system operation and inhibits the transfer of user data.
The invention solves the above problem by using servo mark sub-pattern detection and correlation to detect servo marks. The sub-pattern detection and correlation accurately detects mis-aligned servo marks when the system transitions from one track to another. System operation is improved because servo mark detection failure is reduced resulting in fewer interruptions during user data transfer.
The invention includes disk drive systems, circuitry, and methods of operation. The disk drive system includes a disk device coupled to control circuitry. The control circuitry includes a read channel with a detector that detects servo mark sub-patterns and correlates the detected servo mark sub-patterns to detect a servo mark. The detector includes matched filters to detect the sub-patterns.